Characterization of the Interaction Forces Between Bovine Serum Albumin and Self-Assembled Monolayers

Bich-Van Chu Pham, Chemical Engineering, Purdue University, 480 Stadium Mall Dr., West Lafayette, IN 47907 and Stephen P. Beaudoin, School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907-2100.

The interactions between proteins and various surfaces created using self-assembled monolayers (SAMs) were studied in order to assess factors relating to biocompatibility. Surfaces of interest include bare gold surfaces and gold surfaces coated with SAMs containing a methyl end group (hexadecane thiol), carboxylic end group (mercaptohexadecanoic acid), as well as a bovine serum albumin (BSA) functionalized surface. Cantilever tips functionalized with BSA were brought into contact with these surfaces using atomic force microscopy (AFM) to determine the interaction forces for the BSA/SAM pairs. Using AFM, it is possible to examine the forces that attract/repel proteins from the SAM as the surfaces approach each other as well as the forces that are involved in the actual adhesion of the protein to a surface, which can be observed as the surfaces are brought out of contact. AFM force measurements were taken in both deionized (DI) water and aqueous NaCl solution in order to separate and quantify the influence of the van der Waals (vdW) force and the electrostatic (ES) force. Hamaker constants were determined for each system by modeling the approaching curves in DI water. Zeta potentials were determined for each surface, and the ES force between the interacting surfaces was evaluated. By subtracting the vdW and ES force from the measured pull-off forces, a preliminary estimate of the influence of the hydrophobic/hydrophilic force on the adhesion of BSA to these various surfaces was obtained. By quantifying and isolating these forces, a more exact characterization of how proteins interact with different types of surfaces can be completed, leading to a fuller understanding of biocompatibility.